Tanning



Patented June 29, 1943 7 TANNING Herbert J. West, Old Greenwich, Conn., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application October 25, 1941,

Serial No. 416,493

8 Claims.

This invention relates to the treatment of hides and more particularly to the production of white tanned leathers.

According to the present invention, tanning of hides for the production of white leathers may bay accomplished by impregnating the hides with an aqueous solution of a water-soluble dialkyl ether of dimethylol urea and acidifying the impregnated hides to set or resinify the contained dialkyl ether.

As white tanning agents, any water soluble diether of a monohydric aliphatic alcohol and dimethylol urea may be employed, for, example, the dimethyl, di-ethyl, di-n-propyl, di-iso-propyl and di(ethylene glycol monoalkyl ether) ethers of dimethylol urea. For purposes of the present invention, the crystalline form of the dimethylol urea ethers is preferred, although in some instances the syrupy partially dealkylated dialkyl ethers may likewise be employed. These syrupy products may be obtained by heat treatment of the crystalline diethers in the presence of small quantities of an acid the dissociation constant of which is greater than 1 10- e. g., oxalic, phosphoric acids, etc.

It is an advantage of the process of the present invention that white leathers may be obtained which are fully light fast, give no color reaction with salts of iron and from which the tanning agent is not extractable with water or with dilute acids or alkalies.

In the practice of the invention, the hides to be tanned are drummed in an aqueous solution of sodium chloride and one of the water-soluble dialkyl ethers of dimethylol urea. The drumming is continued until a thorough penetration of the hides with the solution of the dialkyl ether has been effected. The impregnated hides are then acidified by the gradual addition of dilute acid thereto followed by drumming, the acid being preferably added to the hides when present in the tanning bath. Following the acidification, the hides are preferably removed from the drum and allowed to stand for several hours or over night to give the acid additional time to cause setting or resinification of the contained dialkyl ether. The acidity of the hides is then reduced with a dilute solution of sodium bicarbonate applied in the manner customary for neutralizing hides, following which the hides are washed and drained. The tanned hides may then be fatliquored in the usual manner.

The application of the dialkyl ethers of dimethylol urea in the white tanning of hides is illustrated by the following specific example in which parts are by weight.

Example 1 4 3000 parts of pickled goat skin (3 skins) were drummed for two hours in anaqueous tanning bath composed of 3000 parts of a 10% sodium chloride solution and 300 parts of the dimethyl ether of dimethylol urea previously dissolved in water. To the tanning bath was then gradually added about 600 parts of dilute sulfuric acid Two of the tanned skins were washed in cold.

running water for fifteen minutes, drained, fatliquored in the usual manner, set out and dried. The leather was white, full, and well-tanned.

While in the above example 10% of the dialkyl ether ofdimethylol urea on the drained pickled weight of the hides was employed, the quantity of the dialkyl ether may be varied depending upon the weight of the hide to be tanned, the heavier hides requiring more of the dialkyl ether and also a longer drumming time, as will be understood by those skilled in the art.

In place of sulfuric acid, any other sufficiently strong acid may be employed in dilute solution for setting or resinifying the dialkyl'ether contained in the hides, for example, hydrochloric,

phosphoric, formic, lactic, alpha-hydroxy-iso-' butyric, gluconic, citric, oxalic, tartaric, maleic, succinic acids, etc.

In applying the water-soluble dialkyl ethers of dimethylol urea in the tanningprocess, they are preferably first dissolved in water to form a solution thereof before addition to the tanning bath. In some instances it may be found preferable or even necessary to'dissolve the dialkyl ethers in hot water, particularly where they are but slightly soluble in cold water. The solubility tanning process of the present invention may also be applied for the retanning of leathers, for example, to the retanning of formaldehyde, alum, chrome or vegetable tanned leathers.

Example 2 The remaining white tanned skin from Exampie 1 was subjected to formaldehyde tannage in the known manner using 5% of formaldehyde on the drained pickled weight of the skin. The retanned skin showed an increase in heat resistance over the tanned skins of Example 1.

The retanned skin was then..-washed, fatliquored in the usual manner, set. out and dried. The leather was white, full and excellently tanned.

While the process has been more particularly described with reference to the tanning 0f pickled stock, it may be applied in similar manner to 2. In the tanning of hides to make leather, the steps which comprise impregnating the hide with an aqueous solution of the vdimethyl ether of dimethylol urea and acidifying the hide to resinify the ether contained therein.

3. In the tanning of hides to make leather, the steps which comprise impregnating the hide with an aqueous solution of the diethyl ether of dimethylol urea and acidifying the hide to resim'fy the ether contained therein.

4. In the tanning of hides to make leather, the steps which comprise impregnating the hide with an aqueous solution of a dipropyl ether of dimethylol urea and acidifying the hide to resinify the ether contained therein.

5. Leather tanned with a water-soluble diether of a monohydric alcohol and dimethylol urea and containing the same in resinified form non-extractable with water or with dilute acids or alkalies, said leather being obtainable by the process of claim 1.

6. Leather tanned with the dimethyl ether of dimethylol urea and containing the same in rethe spirit and scope' thereof, the foregoing description is intended by way of illustration except as may be defined in the appended claims.

I claim:

1. In the tanning of hides to make leather, the steps which comprise impregnating the hide with an aqueous solution of a diether of a monohydric aliphatic alcohol and dimethylol urea and acidifying the hide to -resinify the ether contained therein.

sinified form non-extractable with water or with dilute acids or alkalies, 'said leather being obtainable by the process of claim 2.

'7. Leather tanned with the diethyl ether of dimethylol urea and containing the same in resinified form non-extractable with water or with. dilute acids or alkalies, said leather being obtain- HERBERT J. WEST. 

